In general, this invention relates to intervertebral spacers and their use to treat spinal defects. More specifically, the present invention is directed to intervertebral spacers composed of a shape memory polymeric material that can be deformed and converted to a desired configuration to facilitate treatment of spinal defects.
Removal of damaged or diseased discs and implantation of intervertebral spacers into the disc space are known medical procedures used to restore disc space height, treat chronic back pain and other ailments. The spacers can be formed of a variety of materialsxe2x80x94both resorbable and non-resorbable materials, including bone-derived material, metallic, ceramic, and polymeric materials. Typically, spacers are pre-formed into a general configuration that is easy to fabricate or, in selected examples, spacers are pre-formed to a generalized configuration that conforms to the vertebral endplates. During surgery, the vertebral endplates must be prepared to receive the spacers. This typically involves either partial or full discectomy to remove the damaged or diseased disc. Thereafter the bone tissue of the vertebral endplates is cut and shaved to receive the spacer. It is also desirable to promote fusion between the vertebral bodies that are adjacent to the damaged or diseased discs. Exposing the cancellous bone tissue in the vertebral body enhances the fusion between the vertebrae. Additionally, an osteogenic material is combined with a spacerxe2x80x94typically packed inside the spacer body and in the disc space around the spacerxe2x80x94to facilitate and promote bone growth.
Preparation of the endplates requires precise cutting to reduce incidences of retropulsion of the preformed spacers and promote bone fusion. The spacers often are designed to interengage the adjacent bony tissue to provide a secure, mechanical interlock with the tissue. A fully seated spinal spacer also helps ensure that any osteogenic material packed into the spacer and surrounding disc space is maintained in intimate contact with the cancellous tissue, which further promotes bone growth. This requires the surgeon to cut the opposing endplates to matingly conform to the upper and lower surfaces of the pre-formed spacers. This can be a very difficult and time-consuming task, and can lead to complications during the operation. It would be preferable to provide a spacer that is self-conforming to the vertebral endplates. However, the implanted spacer must still provide sufficient strength to support the load exerted by the spine without substantial deformation.
To further facilitate implantation of spacers, sufficient clearance between the vertebral bodies must be made available. This is most often accomplished by over-distracting the adjacent vertebrae to provide an enlarged area to work and facilitate implantation of the spacer. While the spacers can be implanted from various directions, including anteriorly, posteriorly and posterior laterally, each of the directions for approach require over-extension of the adjacent vertebrae using distracters. Often a portion of the cortical rim of the upper and lower vertebrae must be cut to provide an entrance into the disc space to insert the spacer. The adjacent vertebrae must be spread apart to provide sufficient room for the surgeon to insert the spacer. This can cause further injury to the already damaged spine. This trauma can also result in over-extension and stretching of associated ligaments and tendons. It would be preferable to reduce over-distraction of the adjacent vertebrae and minimize invasive cutting of the vertebral bodies, yet still be able to insert a spacer sufficient large to restore and maintain a desired disc height.
Thus, in view of the above-described problems, there continues to be a need for advancements in the relevant field, including improved spacers for treatment of spinal defects, methods of fabricating the spacers, and methods of treating spinal defects. The present invention is such an advancement and provides a wide variety of additional benefits and advantages.
The present invention relates to intervertebral spacers, the manufacture and use thereof. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.
In general, this invention provides an expandable spacer for implantation between adjacent vertebrae to treat spinal defects. The spacer can be formed of a shape member polymer (SMP) material and fabricated into a pre-selected configuration. Fabricating the space using a shape memory polymeric material imparts novel and particularly advantageous characteristics to the intervertebral spacer. In a preferred embodiment, the spacer fabricated from an SMP material can be molded into a desired configuration. Curing the polymeric material imprints the original molded configuration to the spacer body. However, when the spacer body is heated above a deformation temperature (Td)xe2x80x94which is usually equivalent to the glass transition temperature (Tg) of the polymeric materialxe2x80x94the SMP becomes elastic. When heated to a temperature equal to or above Td, the spacer body can be deformed to a wide variety of configurations by applying pressure or forcing it into a mold. The spacer body can be xe2x80x9cfrozenxe2x80x9d into the deformed configuration by cooling it below the Td while the body is maintained in the deformed configuration. Thereafter, the deformed spacer body retains the deformed configuration until it is heated above Td. When the spacer body is reheated above Td, the SMP material again becomes elastic; and in the absence of any applied pressure, the spacer body automatically reverts to it original configuration. This process can be repeated any number of times without detrimental effect on the SMP material or the spacer itself.
In one form, the present invention provides a fabricated intervertebral spacer molded to a desired shape and/or size. The spacer comprises a body composed of a polymeric material that exhibits a shape memory defect above a deformation temperature. Above the deformation temperature, the body can be deformed to a first configuration. Preferably, the first configuration provides a reduced external volume or cross-sectional area. Cooling the deformed spacer to a temperature below the deformation temperature, effectively freezes the spacer body in the first configuration. The deformed spacer can then maintain the first configuration until it is desired to cause the body to revert to its original, molded configuration. Most preferably, this occurs after implantation of the deformed spacer into the intervertebral space. Heating the implant spacer above its deformation temperature permits the spacer to revert to its originally molded configuration. Since the deformed spacer can be smaller than the molded spacer, the deformed spacer can be more readily inserted into the disc space using orthoscopic, laparoscopic or other minimally invasive surgical techniques. Additionally, the preferred procedure does not require over-extension of the adjacent vertebral bodies, nor does the preferred procedure require extensive cutting and/or shaping of the cortical rim and vertebral endplates. When desired, preferably after insertion into the disc space, the spacer body is then heated above the deformation temperature. This causes the spacer body to revert to its originally fabricated configuration or a substantially similar configuration.
In one embodiment, the present invention provides an intervertebral spacer for insertion between opposing endplates of adjacent vertebrae. The spacer comprises a body composed of a shaped member polymeric material and has a first upper surface and an opposite lower surface separated from the upper surface by a peripheral sidewall. The body is provided in a first configuration and is capable of being deformed under select stimuli to a second configuration. In the second configuration, the upper plate is adapted to bear against the first endplate of a first vertebra, and the lower surface is adapted to bear against an opposing endplate of an adjacent vertebra.
In another embodiment, the present invention provides an intervertebral spacer for implantation between adjacent vertebrae. The spacer comprising a body having a first bearing surface, an opposite second bearing surface, and a peripheral sidewall therebetween and composed of a shape memory polymeric material, said body capable of withstanding a compressive force of at least 1000 N without significant deformation when maintained at a temperature below a deformation temperature, yet capable of deforming above the deformation temperature.
In still yet another embodiment, the present invention provides a method of orthopedic treatment. The method comprises preparing a disc space between adjacent vertebrae to receive an intervertebral spacer; implanting an intervertebral spacer in the prepared disc space, wherein the spacer is composed of a shape memory polymeric material and is provided in a first configuration exhibiting a first external volume; and subjecting the spacer to a selected stimuli wherein the spacer deforms to a second configuration that exhibits a second external volume greater than the first external volume.
It is one object of the present invention to provide an expanding intervertebral spacer for use in orthopedic treatment.
Further objects, features, aspects, forms, advantages and benefits shall become apparent from the description and drawings contained herein.